<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <!-- 顺序结构 自上而下 -->
    <!-- 选择结构  if语句 switch语句 -->
    <!-- 循环结构 for循环  while 循环-->
</body>
</html>